1. Field of the Invention
This invention relates to a data carrier having a security element blind-embossed by intaglio printing and to a method for producing the data carrier and a printing plate for blind-embossing a security element.
2. Related Art
Data carriers according to the invention are security documents or documents of value, such as bank notes, ID cards, passports, check forms, shares, certificates, postage stamps, plane tickets and the like, as well as labels, seals, packages or other elements for product protection. The simplifying designation “data carrier” and “security document or document of value” hereinafter will therefore always include documents of the stated type.
Such papers, whose market or utility value far exceeds the material value, must be made recognizable as authentic and distinguishable from imitations and forgeries by suitable measures. They are therefore provided with special security elements that are ideally not imitable or only with great effort and not falsifiable.
In the past, particularly those security elements have proved useful that can be identified and recognized as authentic by the viewer without aids but can simultaneously only be produced with extremely great effort. These are e.g. watermarks, which can be incorporated into the data carrier only during papermaking, or motifs produced by intaglio printing, which are characterized by their characteristic tactility that cannot be imitated by copying machines.
It is distinctive for gravure printing that the printing, i.e. ink-transferring, areas of the printing plate are present as depressions in the plate surface. These depressions are produced by a suitable engraving tool or by etching. Before the actual printing operation, ink is applied to the engraved plate and surplus ink removed from the surface of the plate by means of a stripping doctor blade or wiping cylinder so that ink is left behind only in the depressions. Then a substrate, normally paper, is pressed against the plate and removed, whereby ink adheres to the substrate surface and forms a printed image there. If transparent inks are used, the thickness of the inking determines the color tone.
Among gravure printing techniques a distinction is made between rotogravure and intaglio. In rotogravure the printing plates are produced for example by means of electron beam, laser beam or graver. It is distinctive for rotogravure that different gray or color values of the printed image are produced by cells of different density, size and/or depth disposed regularly in the printing plate.
In contrast, in intaglio linear depressions are formed in the printing plates to produce a printed image. In the mechanically fabricated printing plate for intaglio printing, a wider line is produced with increasing engraving depth due to the usually tapered engraving tools. Furthermore, the ink receptivity of the engraved line and thus the opacity of the printed line increases with increasing engraving depth. In the etching of intaglio printing plates, the nonprinting areas of the plate are covered with a chemically inert lacquer. Subsequent etching produces the depressions provided for receiving ink in the exposed plate surface, the depth of these lines depending in particular on the etching time and line width.
The high bearing pressure in intaglio printing causes the substrate material to additionally undergo an embossing that also stands out on the back of the substrate. If the intaglio printing plate is used without inking, the substrate used is subjected to so-called blind embossing, which gives the data carrier a typical surface relief.
Intaglio printing, in particular steel intaglio printing, thus provides a characteristic printed or embossed image that is easily recognizable to laymen and cannot be imitated with other common printing processes. If the engravings in the printing plate are deep enough, a data carrier printed by intaglio acquires through embossing and inking a printed image that forms a relief perceptible by the sense of touch. Steel intaglio printing is therefore preferably used for printing data carriers, in particular security documents and documents of value, for example bank notes, shares, bonds, certificates, vouchers and the like, which must meet high standards with respect to forgery-proofness.
WO 97/48555 discloses a method for producing intaglio printing plates reproducibly by machine. The lines of an original intaglio are detected and the surface of each line precisely determined. Using an engraving tool, for example a rotating graver or laser beam, the outside contour of this surface is first engraved to cleanly border the surface. Then the bordered area of the surface is cleared by the same or another engraving tool so that the total surface of the line is precisely engraved in accordance with the line original. Depending on the form and guidance of the engraving tool, a basic roughness pattern serving as an ink trap for the ink arises at the base of the cleared surface.
It has likewise been proposed to use intaglio printing plates for producing blind embossings. Blind embossings in a metal layer are also known from the prior art. However, known blind embossings are very simple embodiments having only one predetermined embossing height or depth. That is, embossing is effected with a printing plate having only a one-step engraving with a certain constant depth. Embossed areas with different engraving depths, such as lines of different depth, are always spaced apart by unengraved areas. Such embossings are visually recognizable only at certain oblique viewing angles so that this security feature is frequently not perceived by the viewer and attempts at forgery are thus more easily missed. Such embossings are also normally rather unimpressive for the viewer.